Starting apparatus for gas turbines



INVENTOQ 3 Sheets-Sheet 1 Illll;

Jenn D. Hobasom Geonsc seas n Dec. 6, 1960 J. D. HODGSON EI'AL swarms APPARATUS FOR GAS mamas Filed July 18, 1957 nwllww 11] m N I B Mm US A G N R om 8 mm m H7O.- P DA .G m m T s 0 6 9 1 6 D 3 Sheets-Sheet 2 Filed July 18, 1957 lNvzN'roQ Joana D. HobesoN GEORGE Doasou ATTORNEY 1960 J. 0. HODGSON EI'AL 6 ,8 9

STARTING APPARATUS FOR GAS TURBINES Filed July 18. 1957 s Sheets-Sheet s lNveNToQ JOHN D.Ho| e'5o|-l I GEORGE DOBSON.

United States Patent f STARTING APPARATUS FQR GAS TURBINES John Donald Hodgson, Edgware, and George Dobson,

London, England, assignors to The De Havilland Engine Company Limited, Leavesden, Hertfordshire, England, a company of Great Britain Filed July 18, B57, Ser. No. 672,643 Claims priority, application Great Britain July 18, 1956 22 Claims. (Cl. 6tt39.14)

This invention relates to apparatus for starting a gas turbine by imparting rotation through transmission mechanism to its rotor by means of a starting motor, which may be of the turbine, electrical or other type, and has for its object to provide an improved control system for the starting motor.

In starting apparatus for gas turbines, particularly those for aircraft engines, the starting motor has to accelerate the turbine rotor to at least the speed at which the gas turbine becomes self-sustaining, and since it is desirable to maintain the bulk and weight of the starting motor within reasonable limits, the starting motor is usually a high speed motor arranged to be coupled to the rotor of the gas turbine through at least one stage of reduction gearing, with the result that the starting motor itself has to operate at high speed. It is desirable, therefore, to ensure against over-speeding of the starting motor (that is to say against its reaching a speed which might cause it to be subject to damage or mechanical failure), and to this end, to provide in the control mechanism means to prevent much over-speeding not only under normal conditions but especially if a failure should occur, for instance in the transmission mechanism between the starting motor and the turbine motor.

Apparatus for starting a gas turbine engine by imparting rotation to its rotor according to the present invention includes a starter motor arranged to impart rotation to the turbine rotor through transmission mechanism, and torque sensitive apparatus dependant on the torque transmitted by the starter motor through the said transmission mechanism, control mechanism arranged to control the supply of operating power to the starter motor, and an operative connection between said control mechanism and said torque sensitive apparatus which reduces the supply of operating power to the starter motor on a reduction in said torque below a predetermined value. Preferably the supply of operating power to the starter motor is cut off when the torque transmitted by the starter motor falls below the predetermined value.

Thus if, due for example to the faiture of the transmission mechanism between the starting motor and the turbine rotor, the torque being transmitted by the starting motor becomes reduced below a predetermined value, the supply of power of the starting motor will immediately be cut off or so reduced as to ensure that it will not overspeed.

Control means are preferably included which are dependant upon the supply of operating power to said dependant upon the supply of operating power to the "startermotor.

. 2,962,859 1 C6 Patented Dec. 6, 1960 According to a further preferred feature of the invention the torque sensitive apparatus includes an element constituting a reaction member of the transmission mechanism having a limited freedom of movement in the direction of the reaction force applied to it, and resilient means arranged to urge the said reaction member in a direction contrary to the reaction force with a force insuflicient under normal starting torque conditions to resist such reaction force but such that if the reaction force falls below a predetermined value, the reaction member will be moved to actuated apparatus to reduce or cut off the supply of power to the starter motor.

Where the starter motor is in the form of a fluid operated motor, the means for controlling the supply of fluid thereto conveniently includes an operating fluid valve associated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependant on the supply of operating fluid to the starter motor, a torque valve operable by a member sensitive to the torque transmitted by the starter motor through the transmission mechanism and arranged in series with the said pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure sensitive and torque valves to control the said operating fluid valve.

In such an arrangement the torque valve is preferably arranged to be acted upon in one direction by the fluid in the servo system and the torque sensitive member, and in the other direction by a spring, so that during the initial starting period the pressure of the fluid is sufficient to overcome the force of the spring and maintain the valve open until the torque operating through the torque sensitive member is sufficient to do this, and the servo system operates in such a manner that the fluid pressure on the torque valve is relieved after the starter motor attains a predetermined speed so that a reduction in torque below a predetermined value will permit the spring in the torque valve to automatically close the valve.

One form of control apparatus for starting apparatus for a gas turbine and the manner in which it is applied to such starting apparatus is shown somewhat diagrammatically by way of example in the accompanying drawings, in which:

Figure 1 is a diagrammatic side view of the control apparatus in its normal state prior to being brought into operation to start the gas turbine,

Figure 2 is a similar view of the control apparatus in the position it occupies during a starting operation;

Figure 3 is a diagrammatic plan View of part of the epicyclic transmission gearing to which the torque sensitive apparatus is attached, prior to starting the gas turbine,

Figure 4 shows the same parts as Figure 3 in the positions they occupy during a starting operation, and

Figure 5 is a diagrammatic view of the: control appa ratus shown in Figures 1 to 4 applied to the starting apparatus of a gas turbine.

In the arrangement diagrammatically illustrated in Figures 1 to 4 the control apparatus comprises a valve casing 1 containing a piston valve 2 the upper small diameter end 3 of which lies within a bore 4 to the upper end of which air can be supplied through a starting air pipe 5 also communicating through a pipe 5a with a metering orifice controlled by a valve 35 hereinafter referred to. The upper end portion 3 of the valve 2 is arranged to control a port 6 leading via a duct 6a to a port 12 hereinafter referred to, and the valve has three larger diameter portions 7, 8 and 9 of which 8 and 9 lie and move always within a bore 10 while 7 lies normally above the upper end of this bore but under some condi- "tions can enter the-bore 10. The lower end of the valve 2, is acted upon by a light spring 11, tending always to force it upwards. The upper end of the bore is enlarged as shown at 10a and communicates with atmosphere via a passage 7a.

Formed in the bore 10 are ports 12, 13 and 14 of which the port 12 communicates with the port 6 and the ports 13 and 14 communicate with a bore 16 containing a shuttle type piston valve 17 having two piston portions 18 and 19 of which 19 is arranged to control the port 14 and 18 controls a port 20 in direct communication with the pipe 5. A port 15 also leads out of the bore 16. The lower end of the valve 17, 18, 19 is acted upon by a light spring 21 while its upper end is provided with a projection 22 which bears, as shown, on the lower end of a rod 23. A compression spring 24 of relatively large elfective force compared with the spring 21 acts on a collar 25 on the rod 23 so as to tend always to move this rod downwards, while the upper end of the rod 23 acts as shown on one arm 26 of a lever pivoted at 27. A passage 28 leads from a port 29 in the cylinder 16 to the port 13 communicating with the lower end of the cylinder 16. The lower end of the cylinder 10 communicates through a passage 30 and an adjustable needle valve 31 with a passage 32 which also communicates with the passage 30 through a spring loaded non-return valve 33.

The passage 32 communicates with a chamber 34 which communicates with the pipe 5 through the needle valve 35 and with the atmosphere through a vent 35a by way of a valve 36 acted upon in one direction by a spring 37 and in the other direction by an expanding capsule 38 subject to the pressure from a chamber 39 the pressure in which is dependent on the supply of operating power to the starter motor, the chamber 39 thus being for example the chamber immediately in advance of the nozzle ring of a turbine type starter motor (not shown).

The port 15 communicates through a passage 40 with one end of a cylinder 41 containing a piston 42 acted upon by a spring 43 and connected to a valve 44 in such manner that, when air pressure is delivered through the passage 40 to depress the piston 42 the valve 44 brings a passage 45 into communication with a passage 46 to permit starting fluid to be delivered to a turbine type starting motor connected to the gas turbine rotor, for starting purposes.

The lever 26 pivoted at 27 has a second arm 47 which is connected by a knuckle joint 48 to the toothed reaction ring 49 of epicyclic transmission gearing through which the turbine type starting motor is connected to the gas turbine rotor, the ring 49 having limited freedom of rotational movement relative to a fixed casing 50 under the control of spline like projections 51 on the ring 49 lying in slots 52 in the casing 50 as is clearly shown in Figure 3. The arrangement is such that the reaction on the ring 49 due to the starting torque applied by the starting motor tends to move the ring 49 in such a direction as to cause the lever 26 to lift the rod 23 and thus compress the spring 24.

The operation of the apparatus is as follows:

When starting is to be effected operating fluid (herein assumed to be air) is permitted to enter the system through the pipe 5. This first depresses the piston valve 2 against the action of the spring 11 and causes this valve to open the ports 6 and 12 which enables the air to flow via the duct 6 and between the lands 8 and 9 of the piston valve 2 into the duct 28 and thence to the underside of the piston valve 17. The piston valve 17 is therefore moved upwards into the position shown in Figure 2 to bring the port 20 into communication with the port 15 from which the air passes through the passage 40 to the upper side of the piston 42 and thus depresses the valve 44 to permit the supply of working fluid from the passage 45 through the passage 46 to the starting motor.

Upward movement of the piston valve 17 also causes the projection 22 to act on the end of the rod 23 so as to move this rod upwards into the position shown in Figure 2. Such upward movement rocks the toothed ring 49 from the position shown in Figure 3 into the position shown in Figure 4, and, since the valve 44 is now permitting working fluid to flow to the starting motor there is set up in the transmission gearing including the reaction member 49 a torque suflicient normally to maintain the toothed annulus 49 in the position shown in Figure 4 against the action of the spring 24 by way of the lever 26, 47 and the knuckle joint 4-8, even assuming that there is no fluid pressure on the underside of the piston valve 17.

Air from the pipe 5 also flows initially through the pipe 5a and the metering orifice controlled by the valve 35 and thence through the valve 36 to atmosphere.

When the starting motor has been brought into operation a pressure will be set up in the chamber 39 by reason of the back pressure at the turbine nozzles, and this pressure acts on the capsule 38 against the action of the spring 37 so as to close the valve 36. The fluid which can thus no longer escape through the valve 36 and vent 35a to atmosphere is thus forced to pass through the passage 32 and the non-return valve 33 and the passage 30 to the underside of the piston 9 of the piston valve 2 so that the piston valve 2 is returned to its initial position as shown in Figures 1 and 2. This allows fluid in the passage 28 and underside of the piston valve 17 to exhaust to atmosphere via the space between the lands 7 and 8 and the port 7a. The piston valve 17 will nevertheless remain in is upper position as shown in Figure 2 due to the action of the light spring 21 provided the reaction on the toothed ring 49 remains suflicient to compress the spring 24.

If during the starting period, however, the reaction torque exerted by the starting motor on the toothed ring 49 is suddenly reduced below a predetermined value, as for example due to a failure in the transmission mechanism between the starting motor and the gas turbine such as would normally cause the motor to over-speed, then the force exerted on the toothed ring 49 by the spring 24 via the lever 26, 47 will exceed such reaction torque, and the spring 24 will act through the rod 23 to move the ring 49 into the position shown in Figure 3 and to move the piston valve 17 downwards into the position shown in Figure 1. This cuts off the supply of air from the pipe 5 to the port 15 and permits escape of air from the cylinder 41 through the passage 40, the port 15, the port 14 and the port 7a so that the valve 44 moves under the action of the spring 43 to its closed position and thus cuts oil the supply of starting fluid to the starting turbine and prevents its over-speeding.

Moreover, if the apparatus operates in this way during a starting period, due for example to a failure in the transmission mechanism between the starting motor and the gas turbine rotor, the arrangement is such that the valve 2 after returning to its original position cannot again be moved into its starting position until a predetermined time has elapsed so that, should a failure occur during a starting operation and the supply of air through the pipe 5 not immediately be cut off, the starting cycle will not again immediately begin. This is effected by limiting the rate of escape of fluid from the underside of the piston valve 2 to atmosphere through the passages 30 and 32 by means of the needle valve 31.

It will be noted that although a pressure-operated capsule 38 is employed to actuate the valve 36 when the gas turbine speed reaches a predetermined value, the chamber 39 might be in direct communication with the chamber 34, particularly where the fluid operating the starting turbine is air. Where, however, the working fluid for the starting turbine is steam or the decomposition products of hydrogen peroxide whereas air is used in the pipe 5, it may well be desirable to embody an isolating device such as the flexible diaphragm 38 and valve 36 to prevent steam from the decomposition prodl ucts entering parts of the system beyond this capsule and tending to cause rust and/or corrosion.

Normally shutting-off of the starting motor is effected by means which cut off the supply of air or other fluid to the pipe 5 either after a predetermined time or automatically on receipt of an appropriate signal from a speed-responsive device associated with the gas turbine itself, and as this apparatus forms no part of the present invention it will not be further described.

For convenience in Figures 1 to 4 the rod 23 has been shown as acted upon directly by the lever 26 in accordance with movements of the reaction member 49. In practice the connection between the rod 23 and the reaction member 49 may, however, be through a linkage and lever system and for convenience in the diagrammatic illustration in Figure 5 such a system is shown instead of the direct lever connection shown in Figures 1 to 4.

Thus in the arrangement diagrammatically shown in Figured, 53 is the driven shaft of starter mechanism, which shaft during a starting operation will be geared to the gas turbine rotor. The shaft 53 is rigid, as shown, with the spider S4 of epicyclic gearing having planet wheels 55 carried by the spider and each meshing on the one hand with a sunwheel 56 connected to the rotor 57 of the turbine type starter motor 57a and on the other hand with the toothed ring 49 constituting the reaction member shown in Figures 1 and 3. As mentioned, for convenience of illustration in Figure 5, this reaction member 49 is connected to the rod 23 by a lever and linkage system instead of directly, and this lever and linkage system comprises a bell crank lever 58 pivoted at 59 and having one of its arms acted upon by the reaction member 49 while its other arm is pivotally connected to one end of a link 60, a bell crank lever 61 pivoted at 62 through which the link 60 is connected to a link 63, and a lever 26a pivoted at 27a, which may be regarded as the equivalent of the lever 26 in Figure l, by which the link 63 is connected to the rod 23.

The various pipes and other parts of the apparatus shown diagrammatically in Figure 5 are identified by the same numerals as the corresponding pipes and parts in Figures 1 and 2, reservoirs 5b and 45b for the supply of fluid under pressure respectively to the pipe 5 and the pipe 45 being shown, however, in addition in Figure 5.

The casing containing the chamber 34 in Figures 1 and 2 has also been designated 34a, the passage leading from the passage 32. to the chamber 34 has been identified by the numeral 32a, and the casing containing the cylinder 41 has been identified by the reference numeral 41a. It will be readily understood from Figure 5 that the passage 46 communicates with the nozzle ring of the turbine type starter 57a.

It will also be noted that the system embodied in the accompanying drawings could also be used for the control of an electric motor for starting a gas turbine, the valve 44 in such case being replaced by a pressureoperated switch controlling the supply of current to the starting motor. In such a case the pressure-responsive valve 36 and its associated parts including the nonreturn valve 33 might also be omitted.

What we claim as our invention and desire to secure by Letters Patent is:.

1. Apparatus for starting a gas turbine engine by imparting rotation to its .rotor during a starting op'eration, including a starter motor, transmission mechanism through which the starter motor imparts rotation tothe turbine rotor, torque-sensitive apparatus responsive to the torque transmitted by the starter motor to said rotor through said transmission mechanism, control mechanism arranged to control the supply of operating power to the starter motor, inter-connecting means normally actuated during said starting operation by said torquesensitive apparatus to cause said control mechanism to reduce the supply of operating power to the starter 6 motor when the magnitude of said torque is less than a predetermined value, and biassing means which renders the inter-connecting means temporarily inoperative at the commencement of said starting operation during a time interval suflicient to permit said torque to rise above said predetermined value.

2. Apparatus for starting a gas turbine engine, as claimed in claim 1, including timing means arranged to terminate the operation of said biassing means after the expiry of said time interval.

3. Apparatus for starting a gas turbine engine, as claimed in claim 2, including control means which is responsive to the supply of operating power to the starter motor and which renders said biassing means operative upon connection of such supply.

4. Apparatus as claimed in claim 3, including delay apparatus arranged to prevent re-operation of said biassing means before the expiry of a predetermined time period after the termination of the operation of the biassing means, whereby the delay apparatus prevents a second starting operation from being initiated until said time period has elapsed.

5. Apparatus as claimed in claim 4 in which the torque sensitive apparatus includes an element constituting a reaction member of the transmission mechanism having a limited freedom of movement in the direction of the reaction force applied to it, and resilient means arranged to urge the said reaction member in a direction contrary to the reaction force with a force insufficient under normal starting torque conditions to resist such reaction force but such that if the reaction force falls below a predetermined value, the reaction member will be moved to actuate said control mechanism to reduce or cut-off the supply of power to the starter motor.

6. Apparatus as claimed in claim 5 in which the starter mo or is in the form of a fluid operated motor, and said control mechanism includes an operating fluid valve associated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependent on the supply of operating fluid to the starter motor, a torque valve operable by said reaction member and arranged in series with the said pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure sensitive and torque valves to control the said operating fluid valve.

7. Apparatus as claimed in claim 6 in which during said commencement of said starting operation, the torque valve is arranged to be acted upon in one direction by the fluid in the servo system and in the other direction by a spring, so that during said commencement the pressure of the fluid constitutes said biasing means and is suflicient to overcome the force of the spring and maintain the valve open until the torque operating through the torque sensitive member is sufficient to do this.

8. Apparatus as claimed in claim 1 in which the torque sensitive apparatus includes an element constituting a reaction member of the transmission mechanism having a limited freedom of movement in the direction of the reaction force applied to it, and resilient means arranged to urge the said reaction member in a direction contrary to the reaction force with a force insufficient under normal starting torque conditions to resist such reaction force but such that if the reaction force falls below a predetermined value, the reaction member will be moved to actuate said control mechanism to reduce or cut-off the .supply of power to the starter motor.

, 9. Apparatus as claimed in claim 8 in which the starter motor is in the form of a fluid operated motor, and said control mechanism includes an operating fluid valve as sociated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependent on the supply of operating fluid to the starter motor, a torque valve operable by said reaction member and arranged in series with the said pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure 7. sensitive and torque valves to control the said operating fluid valve.

10. Apparatus as claimed in claim 9 in which, duringsaid commencement of said starting operation, the torque valve is arranged to be acted upon in one direction by the fluid in the servo system and in the other direction by a spring, so that during said commencement the pressure of the fluid constitutes said biasing means and is sufficient to overcome the force of the spring and maintain the valve open until the torque operating through the torque sensitive member is suflicient to do this.

11. Apparatus as claimed in claim 1 in which the starter motor is in the form of a fluid operated motor, said control mechanism includes an operating fluid valve associated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependent on the supply of operating fluid to the starter motor, a torque valve operable by said reaction member and arranged in series with thesaid pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure sensitive and torque valves to control the said operating fluid valve.

12. Apparatus as claimed in claim 11 in which, during said commencement of said starting operation the torque valve is arranged to be acted upon in one direction by the fluid in the servo system, and in the other direction by a spring, so that during said commencement the pressure of the fluid constitutes said biasing means and is suflicient to overcome the force of the spring and maintain the valve open until the torque operating through the torque sensitive member is sufiicient to do this.

13. Apparatus as claimed in claim 2 in which the torque sensitive apparatus includes an element constituting a reaction member of the transmission mechanism having a limited freedom of movement in the direction of the reaction force applied to it, and resilient means arranged to urge the said reaction member in a direction contrary to the reaction force with a force insuflicient under normal starting torque conditions to resist such reaction force but such that if the reaction force falls below a predetermined value, the reaction member will be moved to actuate said control mechanism to reduce or cut-oft" the supply of power to the starter motor.

14. Apparatus as claimed in claim 13 in which the starter motor is in the form of a fluid operated motor, and said control mechanism includes an operating fluid valve associated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependent on the supply of operating fluid to the starter motor, a torque valve operable by said reaction member and arranged in series with the said pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure sensitive and torque valves to control the said operating fluid valve.

15. Apparatus as claimed in claim 3 in which the torque sensitive apparatus includes an element constituting a reaction member of the transmission mechanism having a limited freedom of movement in the direction of the reaction force applied to it, and resilient means arranged to urge the said reaction member in a direction contrary to the reaction force with a force insufficient under normal starting torque conditions to resist such reaction force but such that if the reaction force falls below a predetermined value, the reaction member will be moved to actuate said control mechanism to reduce or cut-off the supply of power to the starter motor.

16. Apparatus as claimed in claim 15 in which the starter motor is in the form of a fluid operated motor, and

said control mechanism includes an operating fluid valve associated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependent on the supply of operating fluid to the starter motor, a torque valve operable by said reaction member and arranged in series with the said pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure sensitive and torque valves to control the said operat ing fluid valve.

17. Apparatus as claimed in claim 2 in which the starter motor is in the form of a fluid operated motor, and said control mechanism includes an operating fluid valve associated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependent on the supply operating fluid to the starter motor, a torque valve operable by said reaction member and ar ranged in series with the said pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure sensitive and torque valves to control the said operating fluid valve.

18. Apparatus as claimed in claim 3 in which the starter motor is in the form of a fluid operated motor, and said control mechanism includes an operating fluid valve associated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependent on the supply of operating fluid to the starter motor, a torque valve operable by said reaction member and arranged in series with the said pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure sensitive and torque valves to control the said operating fluid valve.

19. Apparatus as claimed in claim 4 in which the starter motor is in the form of a fluid operated motor, and said control mechanism includes an operating fluid valve associated with a fluid servo system which includes a pressure sensitive valve subject to a pressure dependent on the supply of operating fluid to the starter motor, a torque valve operable by said reaction member and arranged in series with the said pressure sensitive valve, and fluid servo apparatus controlled jointly by the said pressure sensitive and torque valves to control the said operating fluid valve.

20. Apparatus as claimed in claim 7 in which said timing means arranged to terminate the operation of said biassing means comprises pressure-relieving apparatus which relieves said fluid pressure on said torque valve after the expiry of said time interval.

21. Apparatus as claimed in claim 10 in which said timing arranged to terminate the operation of said biassing means comprises pressure-relieving apparatus which relieves said fluid pressure on said torque valve after the expiry of said time interval.

22. Apparatus as claimed in claim 12, in which said timing means arranged to terminate the operation of said biassing means comprises pressure-relieving apparatus which relieves said fluid pressure on said torque valve after the expiry of said time interval.

References Cited in the file of this patent UNITED STATES PATENTS 2,187,120 Gosel'an et a1 Jan. 16, 1940 2,516,911 Reggio Aug. 1, 1950 2,562,742 Rowe et al July 31, 1951 2,614,798 Rubbra Oct. 21, 1952 2,737,776 Strough Mar. 13, 1956 2,742,757 Jaquith Apr. 24, 1956 2,764,272 Reynolds Sept. 25, 1956 l i i j i i 

